Nonwoven sheets made from rectangular cross section monofilaments

ABSTRACT

Nonwoven sheets of continuous synthetic polymer, e.g., stereoregular polypropylene, monofilaments which have elongated, e.g., rectangular, cross sections with aspect ratios of at least about 3:1 and are disposed randomly and are substantially discrete from each other except at crossover points in the sheet. These sheets may be made by extruding the polymer through appropriately shaped orifices, partially cooling the resulting monofilaments, drawing them with a pneumatic jet and depositing them on a collecting device.

ilnited States Patent 72] Inventor Phillip 11. Parker San Rafael, Calif.

[21 App]. No. 845,075

[22] Filed July 25, 1969 [45] Patented Dec. 28, 1971 [73] Assignee Chevron Research Company San Francisco, Calif.

[54] NON WOVEN SHEETS MADE FROM RECTANGULAR CROSS SECTION MONOFILAMENTS 5 Claims, No Drawings [52] US. Cl 161/72, 161/92, 161/150, 161/157, 161/165, 161/177, 264/174, 264/177 51] 1nt.C1 D01d 5/22, D01d 7/00, B32b 27/02 [50] Field of Search 264/177 F, 179;161/l50, 157,177, 72, 89, 92, 252,165 [56] References Cited UNITED STATES PATENTS 3,533,904 10/1970 Jurkiewitsch 161/177 X 3,547,763 12/1970 Hoffman 161/177 X 2,456,922 12/1948 Cogovan 161/177 X 2,620,853 9/1952 161/150 X 2,825,120 3/1958 161/177 3,109,220 11/1963 McKinney et al. 161/177 X 3,109,278 11/1963 Gibson 161/177 3,164,949 1/1965 Pitzl 161/177 X 3,322,607 5/1967 Jung. 161/150 X 3,360,421 12/1967 Sands 161/150 X 3,396,071 8/1968 Couzens. 161/150 3,402,548 9/1968 Wininger et a1. 57/140 3,492,389 1/1970 Port et a1. 264/147 Primary Examiner-Harold Ansher Attorneys-A. L. Snow, F. E. Johnston and John Stoner, .lr.

ABSTRACT: Nonwoven sheets of continuous synthetic polymer, e.g., stereoregular polypropylene, monofilaments which have elongated, c.g., rectangular, cross sections with aspect ratios of at least about 3:1 and are disposed randomly and are substantially discrete from each other except at crossover points in the sheet. These sheets may be made by extruding the polymer through appropriately shaped orifices, partially cooling the resulting monofilaments, drawing them with a pneumatic jet and depositing them on a collecting device.

NONWOVEN SHEETS MADE FROM RECTANGULAR CROSS SECTION MONOFILAMENTS FIELD OF Tl-IE INVENTION This invention concerns nonwoven sheets made from continuous synthetic polymer monofilaments which have elongated cross sections. More particularly, it relates to such sheets in which themonofilaments have substantially rectangular cross sections and are discrete from each other except crossover points.

BACKGROUND THE lNYENTlON strengths of the filaments. The strengths of such freshly spun monofilaments have been improved by drawing then between rolls rotating at different speeds. More recently they have been drawn by spin drawing techniques. In spin drawing" partially cooled, partially crystalline filaments are fed-into a,

pneumatic jet. The jet works on the ejector principle. That is, the expanding gaseous medium passing through thejet carries and accelerates the filaments causing then to be drawn or oriented.

Developments concerning methods for depositing the drawn filaments have been directed towards improvingthe isotropic properties of the finished, nonwoven product made from the filaments. Such developments have usually concerned particular patterns for laying the drawn filaments down on the collecting surface for keeping the filaments discrete, i.e., not entangled or bundled.

For the most part filaments which have been used to make nonwoven sheets have had circular cross sections. Certain noncircular cross section filaments have been suggested as equivalent to circular cross section filaments for use in nonwoven materials. In the related yarn art noncircular cross section monofilaments have been used to simulate natural fiber shapes, provide a particular appearance or increase covering power. l-leretofore, it has not been recognized that the crosssectional shapes of the filaments may materially affect the ten- I sile properties of finished nonwoven sheets made therefrom.

INVENTION DESCRIPTION It has been found that nonwoven sheets of continuous oriented synthetic polymer monofilaments having an elongated cross section in which the aspect ratio is at least about 3:1 and in which the monofilaments are deposited randomly and are substantially discrete from each other except at crossover points have unexpectedly better tensile properties than corresponding sheets of circular cross section monofilaments. This finding is especially surprising in view of the fact that individual monofilaments of circular cross section and in dividual monofilaments of elongated cross section and comparable denier have substantially similar tensile properties.

Filaments having elongatedcross sections are used to make the unexpectedly strong nonwoven sheets of this invention. These filaments are characterized as having an aspect ratio (the ratio of cross section length of cross section width)' of at least about 3:1 and usually in the range 3:l and about 8:1 The shape of the cross section of these filaments will usually be substantially rectangular. Substantially rectangular cross sections include those having two sets of essentially parallel flat surfaces which intersect each other essentially at 90 angles (true rectangle) as well as those having two slightly rounded oppositely disposed planar surfaces, the respective ends of which are joined by rounded, smaller surfaces. These latter cross sections are characterized as elliptical. The surfaces of these filaments will be substantially regular. That is, they should be relatively smooth and free of large bumps, protrusions or lobes.

The particular shapes of the elongated cross section monofilaments used in this invention aredependent upon the shaped of the orifice or die from which they are spun and extent to which they are oriented or drawn. Oriented monofilaments of elliptical cross sections are formed by extruding the polymer melt from orifices having a substantially rectangular cross section. Such monofilaments emerge from the orifices with rectangular cross sections; but, as they are drawn their cross sections reshape to ellipses. Oriented monofilaments which are substantially rectangular are made by spinning the melt from a die of rectangular cross section in which the longitudinal sides are somewhat concave. When such monofilaments are drawn the concave sides of the rectangle flatten so that they are substantially parallel. Devices for making elongated cross section monofilaments are well known. See for instance U.S. Pat. No. 3,179,770.

The freshly spun monofilaments are drawn from an original cross-sectional area as the filament emerged from the die of about 0.004 to 4.0 mm. down to a cross-sectional area of about 0.00005 to 0.008 mm]. In terms of a circular filament this is equivalent to reducing the diameter from about 0.l0l.0 mm. down to l0-l00 microns (1 to 60 denier). This drawing is done after the filaments are partially cooled and tenacities 'of about 2 to 5 g. per denier and elongations of about 50 to 400 percent, depending, of course, upon the particular drawing conditions.

The drawing orients the polymer structure and greatly increases the filaments tensile strength. While roll drawing or spin drawing may be used, it is preferable to spin draw the monofilaments used to make the unique, nonwoven sheets of this invention.

Accordingly, the freshly spun monofilaments are fed, usually in a bundle of about 5*500, into the main chamber of a pneumatic jet. Air, or other inert gases may be used as the gaseous drawing medium. In order to draw the monofilaments sufficientlythe air velocity will usually be about 200-800 m. per sec. within the main chamber. Air travelling at these velocities will pick up the monofilament bundle and draw the filaments atspeeds in excess of 1,500 in. per min. and up to the speed which causes the filaments to break. The draw rate will preferably range between 2,500-5,000 m. per minute. Particular jet designs may be used to keep the individual monofilaments separate while they pass through the jet. Other techniques, such as charging the filaments, may also be used to keep then from entangling.

The thus drawn monofilaments may be laid down onto a collecting surface as they emerge from the pneumatic jet. If the filaments have been drawn over rolls instead of spin drawn they may be passed into a pneumatic filament-handling device. Such devices are well known and operate on the same principle as the pneumatic spindrawing jet. However, the gas velocities are below those whichstretch the filaments in the handling device. lnorder to keep the gas emerging from the jet with the filaments from entangling the filaments as they are deposited on the collecting surface or from blowing them off the surface, the surface may be a wire screen or other porous medium which allows the gas to pass through it.

Withdrawal and/or dissipation of the high-velocity gas emerging from the jet may be facilitated by applying suction to the side of the porous collecting surface opposite that on which the filaments are being laid.

The collecting surface will move away from the zone in which the bundles of nonentangled substantially parallel filaments are laid down. This motion away from the lay down zone may be conveniently achieved by using an endless moving screen belt as the collecting surface. In order to form webs having substantially isotropic tensile properties the rate at which the filaments are forwarded onto the collecting surface will be several times that at which the surface is moving away from the lay down zone. Usually, the filament forwarding speed will be about -1000 times the speed at which the surface is moved away from the lay down zone.

Filament patterns in the laid-down web will depend upon the relative motion of the filaments and the collecting surface. By moving the lay down device transverse to the direction of the take away or by keeping the lay down device stationary and moving the filaments either by oscillating the lay down device or baffling the filaments, various filament patterns will be achieved. The pattern should not be such as to affect substantially the isotropicity on the laid-down web. It is within the scope of this invention to incorporate within the nonwoven sheets a variable amount of monofilaments having a nonelongated cross section shape; provided such added filaments do not entirely eliminate the improved strength properties obtained through the use of elongated cross section fibers in accordance with this invention. Such fibers of other shapes affect other properties of the sheet as well as the strength of it. In particular, fibers having a round or circular cross section may be incorporated into the nonwoven sheet. The presence of such circular fibers improves the hand of the resulting sheet by reducing the stiffness thereof. By a proper choice in the ratio of round to elongated fibers, sheets having both improved hand and high strength may be obtained.

The thus laid web of continuous monofilaments of elongated cross section is dryand even in this form has superior tensile properties relative to corresponding webs of circular cross section monofilaments.

Weight of the webs of this invention normally ranges from about 0.5 to 44 ounces per square yard. Their densities will usually be about 0.2 to 0.7 g. per cc. They will normally be 0.005 to 0.3 inch thick.

This web or batt is useful as such for insulation, paper reinforcement, nonwoven fabric reinforcement and filters. It may be further treated if desired by needle punching, calendering, heat sealing, sewing or knitting depending upon its intended end use. This web is also susceptible to other conventional treatments such as adhesive bonding. These bonded webs are useful as carpet backing, sacking, paper and fabric reinforcement, felt carpets, nonwoven fabrics, etc. As a general rule, the finished nonwoven product with the elongated cross section filaments have superior tensile properties to corresponding products made from conventional monofilaments.

The synthetic polymers which may be used in this invention are those which may be spun or otherwise formed into continuous monofilaments. Such polymers include crystalline polypropylene, crystalline polyethylene, poly-4-methyl-1-pentene, copolymers thereof, polyvinylchloride, polyesters such as polyethylene terephthalate, polyamides such as nylon and the like.

EXAMPLES The following examples illustrate the nonwoven sheets of this invention. These examples are not intended to limit the invention in any manner. Unless otherwise indicated, percentages are by weight.

EXAMPLE 1 Commercial, substantially crystalline, stereoregular polypropylene with a melt fiow rate of 4 was melted in an extruder with the final extruder zone having a temperature of 320 C, It was then melt spun through a two-hole spinnerette having round holes with a diameter of 1.0 mm. The spinnerette temperature was 300 C. The polymer was extruded at a rate of 4.1 g./hole/minute. The resulting circular cross section filaments then fell 32 feet to a pneumatic jet which accelerated the filaments to a linear velocity of 2.400 yards per minute thereby drawing them. The filaments were then collected on a screen with a vacuum behind it to form a web or batt. This batt was slightly compressed between two rollers for easier handling.

The tenacity ofthese filaments, the breaking strength of this web or batt were determined by conventional ASTM tests. These properties are tabulated in tables land II, respectively.

EXAMPLE 2 Filaments and a batt were prepared under conditions similar to those of example 1 except that the filaments were accelerated by the pneumaticjet to 5,200 yards per minute after being melt spun. The tenacity of these filaments and the break strength of this are also shown in tables land 11.

EXAMPLE 3 Filaments and a batt were prepared under conditions similar to those of example 2 except that the filaments were extruded at a rate of 3.3 gJhoIe/minute and were accelerated by the pneumaticjet to 5,300 yards per minute. The tenacity of these filaments are shown in table 1 and batt breaking strength in table 11.

EXAMPLE 4 Filaments and a batt were prepared under conditions similar to those in example 1 except that the spinnerette had 3 rectangular orifices which were 3 .0 mm. long and 0.3 mm. wide. The filaments were extruded at a rate of 2.8 g./hole/minute and were accelerated by the pneumatic jet to 2,200 yards per minute. The filament properties are shown in table I and batt properties in table 1].

EXAMPLE 5 Filaments and a batt were prepared under conditions similar to those of example 4 except that the filaments were accelerated by the pneumatic jet to 4,000 yards per minute. Filament properties are shown in table I and batt properties in table 11.

EXAMPLE 6 Filaments and a batt were prepared under conditions similar to those of example 4 except the filaments were extruded at a rate of 3.3 g./hole/minute and accelerated by the pneumatic jet to 4,600 yards per minute. Filament properties are shown in table 1 and batt properties in table 11.

EXAMPLE 7 Filaments and a batt were prepared under conditions similar to those of example 4 except that the spinnerette had 3 rectangular orifices which were 2.0 mm. long and 0.5 mm. wide. The filaments were extruded at a rate of 3.3 g./hole/minute and were accelerated to 5,200 yards per minute by the pneumatic jet. Filament properties are shown in table I and batt properties in table [1.

EXAMPLE 8 The nonwoven batt of example 1 was passed through a needle loom to produce a needled felt with about 200 needle penetrations per square inch. The results of a breaking strength test on the resulting fabric are shown in table 11].

EXAMPLE 9 The nonwoven batt ofexample 4 was needle felted as in example 8. The results of a breaking strength test on the resulting fabric are shown in table lll.

EXAMPLE 10 The nonwoven batt of example 3 was pressed in a hot calendering machine at about C. to heat seal the fibers together. The breaking strength of the heat-sealed nonwoven fabric is shown in table IV.

manner similar to example ID. The breaking strength of the heat-sealed nonwoven fabric is shown in table iv.

lclaim: l. Nonwoven sheet of continuous synthetic polymer monofilaments, said monofilaments having elongated cross sections in which the aspect ratio is in the range of 3:1 to 8:l

and said monofilaments being disposed randomly and substan- EXAMPLE l2 tially discrete from each other except at crossover points.

2. The nonwoven sheet of claim 1 wherein the cross sections The nonwoven batt of example 6 was heat sealed in a of the monofilaments are substantially rectangular. manner similar to example 10. The breaking strength of the 3. The nonwoven sheet of claim 1 wherein the individual heat-sealed nonwoven fabric is shown in table IV. cross-sectional areas of the monofilaments are about 0.0005

TABLE L-PROPERT1ES or RECTANGULAR ANl) ltUUNl) FILAMEN'PS Fihnnent Filament. I cross snrlnee Fllnnu-nt l)ie section area, Filacross cross ratio microns I Filament oi Filament ment section, section, length micron Tenacity, Example No. shape denier microns mm. width length gJdcniel 1 Round 16.6 51 1. 160 2.7 2 ...do 7.8 1. 110 3.11 3 o.. 6.8 33 1. 103 3.5 4 Rectangular" 12.6 75 x 26 0.3 x 3. 202 2.5 5 ,.d0 6.9 59 x17 0.3 x 3. 152 3.9 7.1 50 x 21 0.3 x 3. 142 3.8 6. 2 x 24 0.5 x 2. 128 4.0

D ROUND FILAMENTS Filament Filacross Die cross Breaking Filament ol' Filament ment section, section, Batt load, Example No. shape denier microns mm. oz./yd: lb./in.

51 1.0 3. 5 l. n 33 l. I) 4. 5 0.33 75 x 26 ll. 3 X 3.0 3. 7 8. (i 5!] x 17 ll. 3 x 3. ll 3. 5 5. 0 x 2i ll. 3 X 3. ll 4. 5 l. .l 40 x 24 (l. 5 x 2. 0 4. 6 1. 26

TABLE lll.liREAKlN(l LOADS ()N NEEDLE FELTEI) liAT'l FROM REP- IANGULAR ANl) ROUND FILAMENIS Filament Nonwoven Filzicross llic cross lint-t, Breaking butt of Filament nn-nlv section, section, weight, lOiili, Example No. shape denier microns nnn. o7../ v(l. lI)./in.

l'l Round..... 16.0 5i L0 2.7 ii ll. 12.6 75 x iii 0. 3 X 3. (l 3. ll 22 Rectangular.

TABLE iV.BREAKING LOAl) OF lie-at scaled Filament nonwoven File cross l)ic cross Shcct. Breaking fabric of Filament ment section, section, weight, load. Examplc No. shape denier microns mm. oz./yd. ll)./m.

6. 8 33 1. 0 4. 2 2. 4 0.4 40x24 0.5x2.0 4.2 l0.li 7.6 50x21 0.3x3.0 4.2 20.7

The tenacity data in table 1 indicate there is no significant to 0.008 mm.". difference in tenacity between round filaments and rectangu- 4. The nonwoven sheet of claim 1 wherein the polymer is lar filaments of comparable denier and orientation. in contrast the strength data reported in tables ll through lv illustrate that various types of nonwoven sheets made from rectangular cross section monofilaments have substantially better breaking strength than similar sheets made from comparable circular cross section monofilaments. 

2. The nonwoven sheet of claim 1 wherein the cross sections of the monofilaments are substantially rectangular.
 3. The nonwoven sheet of claim 1 wherein the individual cross-sectional areas of the monofilaments are about 0.00005 to 0.008 mm.2.
 4. The nonwoven sheet of claim 1 wherein the polymer is substantially crystalline, stereoregular polypropylene.
 5. The nonwoven sheet of claim 1 wherein the polymer is substantially crystalline, stereoregular polypropylene, the cross sections of the monofilaments are substantially rectangular and have individual areas of about 0.00005 to 0.008 mm.2 and the aspect ratio is in the range of 3:1 and 8:1. 